Process for the gaseous deoxidation of anode copper



Dec. 8., 1970 N, J. THEMIELIISI ErAI. 3,545,962

PROCESS, FOR THE GASEOUS-DEOXIDATION OF ANODEQ COPPER Filed Ap;'i1 5, 1967 -3 Sheets-Sheet 1 n a q N 6 cu .n i N 1 N a N y l llpuuufllln111111111111! Q g *2 2st v n x u n C) K m N/CKOLAS z]. THKMIEL/S PAUL R. SCHMIDT Dec. 8., 1970 v N; J. THEMELls ET-AL 3,545,962

PROCESS FOR THE GASEOUS DEOXIDATION OF ANODE COPPER Filed April 5, 1967 3 Sheets-Sheet 2 [u $1 5 o l '9 MCKOLAS u. THE/MEL /& PAUL R SCHM/DT Dec. 8, 1970 v T|- L s ET AL 3,545,

PROCESS FOR THE GASEOUS DEOXIDATION OF ANODE COPPER Filed April 5, 1967 5 Sheets-Sheet 5 /V/6/(0LA6 THE PAUL R. SCHM/DT EL/S United States Patent U.S. C]. 75-76 Claims ABSTRACT OF THE DISCLOSURE A process for the gaseous deoxidation of molten copper in which a reformable hydrocarbon and steam is substantially simultaneously injected beneath the surface of molten metal in a furnace through water cooled lances in which partial reforming of the hydrocarbon with the water vapour to carbon monoxide takes place in the lance prior to its introduction into and dispersion within the molten copper in the furnace.

This invention relates to the treatment of molten metal and more particularly to the treatment of molten metal to deoxidize the same. It is of especial value in connection with the treatment of molten copper and copper-base alloys (herein generically referred to as copper-base metals) and will therefore be described with particular reference to that case. It is however to be appreciated that the processes and apparatus herein described are of value also in the deoxidation of other molten metals.

The solubility of oxygen in copper increases rapidly as the copper is raised above its melting point. Accordingly it is a standard practice in the production of copper base metals to subject the metal, while in the molten condition, to a treatment which will reduce, or even eliminate, the oxygen content. A well known technique which has been practised for very many years is that known as poling and consists in immersing poles of green wood in the colten copper base metal. The volatilisation of gases from the green wood creates substantial turbulence in the molten metal and the general effect is one of chemical reduction.

In order to simplify and decrease the cost of the deoxidizing operation, means have been sought to introduce into the molten metal a gas which has reducing properties, either directly or by generation from an introduced solid substance.

One method which has been proposed in U.S. Pat. No. 2,989,387, issued June 20, 1961 to Kuzell et al., consists in injecting into a molten metal a gaseous mixture containing carbon monoxide and hydrogen, both of them reducing gases, Such a gaseous mixture may be obtained by subjecting a hydrocarbon to partial oxidation, the carbon being converted to carbon monoxide and the hydrogen being released as molecular hydrogen. Provision is made for such oxidation to be effected as an operation separate from the metal-treating operation itself. Gases are commonly injected into molten metals by the use of lances or tuyeres and in the method just referred to the gas brought to the lance or tuyeres is already a gaseous mixture containing carbon monoxide and hydrogen.

It is an object of one aspect of the present invention to provide a process for the deoxidation of molten metals, and particularly copper-based metals which makes use of hydrocarbon starting materials but avoids the necessity for a separate unit for the partial oxidation or reforming with water vapour of the hydrocarbon prior to its introduction into the furnace. It is based on the discovery that hydrocarbons may be readily reformed to carbon "Ice monoxide and hydrogen by premixing Water vapour with the hydrocarbon so that the mixture of the reducing gases can be produced either within the injection lance or as the hydrocarbon-water vapour mixture is dispersed within the liquid bath.

Therefore, the process for the deoxidation of molten copper of the present invention involves producing and bubbling reducing gas mixtures through the melt with an injection lance, which lance is disclosed and referred to herein for a clear understanding of the process of the present invention. A feature of the present process is that the reducing gases are obtained by chemical reaction within the lance structure, and also in the melt, and at the same time the formation of excessive carbon either inside the lance or later after the gases have been bubbled through the melt is clearly inhibited if not prevented. It is a known fact that without the process described herein hydrocarbons such as propane and butane injected into a copper melt, produce an excessive amount of carbon by thermal decomposition at the high temperatures experienced in normal copper refining. This carbon may build up in the lance and results in partial or complete blockage and also pollutes the atmosphere around the furnace with thick, black smoke which constitutes a health and safety hazard.

A further feature of the present process is that the heat required for the chemical reaction within the lance, and also the heat required to heat the gases to the reaction temperature, maintains the lance cooler than the melt so that a lance material may be used which could not otherwise withstand the high temperatures experienced in the deoxidation processes.

The raw feed materials which may be used in the present process are water vapour (steam) mixed with the appropriate proportion of hydrocarbons such as methane, propane, butane, naphtha.

According to the present invention there is provided a process for the deoxidation of molten metal which comprises injecting into a bath of said molten metal below the upper surface of said bath a mixture of a reformable hydrocarbon and steam whereby to achieve partial reforming thereof in situ to a reducing gas mixture containing carbon monoxide and hydrogen.

In the drawings:

FIG. 1 is a side view of a typical rotary furnace with cut-away section showing a lance depending into the melt;

FIG. 2 is a section of a reverberatory furnace with a lance extending through a side port thereof into the melt; and

FIG. 3 is a cut-away section of the lance which is associated with the process of the present invention and illustrates the flow of the water-gas mixture therein.

In a particularly preferred form of the said process the metal is a copper-based metal.

While it is not desired to be limited to any particular theory, it is believed that the gas issuing from the injection lance below the surface of the metal melt is caused to disintegrate into a plurality of small bubbles a short distance from the nozzle or orifice of the injection lance.

V The high interfacial area results in very high rates of may be effected as the gases move through the lance (itself heated by the surrounding molten metal) and the gaseous mixture emerging from the lance into the body of molten metal comprises a substantial proportion of carbon monoxide and hydrogen.

The efiiciency of the deoxidation of the molten metal will depend inter alia on the establishment of a considerable contact area between the injected gas and the molten metal. For this reason the design of the lance and the velocity of supply of the gas should preferably be such that the gas issuing from the lance breaks up to form a mass of small bubbles (rather than a relatively few large bubbles) at a few inches away from the lance orifice. This condition is attained when the Reynolds number of the gas flow through the orifice at the top of the lance is greater than 2,100.

While it is generally preferred that the hydrocarbon used should be gaseous at ordinary temperatures, e.g., it may be methane, ethane, propane, butane or isobutane, hydrocarbons which are liquid at ordinary temperatures, e.g., naphtha or light oils may also be used.

The preferred hydrocarbons for use are methane, ethane, propane and butane.

The proportion of steam flow to hydrocarbon flow used may be adjusted to be equal to or less than the stoichiometric amount suflicient to reform the hydrocarbon to carbon monoxide and hydrogen. If the rate of travel of the mixture through the lance is higher, so that the mixture does not heat up sufficiently rapidly to promote the interaction of the hydrocarbon and the steam to a sutficient extent, there may be included in the mixture a proportion of oxygen, to facilitate the oxidation of the hydrocarbon. Such added oxygen will normally react exothermically thus adding heat to the flowing mixture. However, care must obviously be taken to avoid the addition of so much oxygen that any important proportion of it reaches the molten metal unchanged as that would defeat, or tend to defeat, the object of the deoxidation process.

It will be appreciated that added oxygen may be provided in the form of air and that if desired the injected gas stream may contain other, generally inert, gases such as nitrogen or argon. It is also possible to include in the injected gas stream other agents known per se to have a desirable conditioning effect on the molten metal.

The process of the present invention may be applied, for example, to the deoxidizing of molten copper which is intended for use as electrical anode copper or for the production of wire-bars, in reverberatory furnaces of conventional design, or in cylindrical tilting anode furnaces such as are normally used with the poling technique referred to above, without any important modification of the furnaces. Thus for example, any of the following procedures may be used:

(a) A battery of lances having the structure disclosed herein (e.g., 4-6) may be used for injecting gas to the melt over a period of time comparable to the normal poling period (2-3 hours). At the end of the injection period the metal can be cast.

(b) A battery of lances (e.g., 2-3) can be used for reducing the metal near the tapping hole for a period of 30-45 minutes, following which the metal is cast while continuing the reduction during the whole casting period. Thus, metal flowing toward the tap-hole must pass through and mix with the highly-reduced metal in the tapping zone. This method is in some respects preferable to (a) above, since it decreases the overall time of treatment in the furnace and requires less apparatus.

(c) A variation of the above processes requires a small (e.g., -ton) holding furnace interposed between the reverberatory furnace and the casting machine. Lances, orifices, or tuyeres then introduce the reducing gas in this holding furnace during the entire casting period. This alternative is of particular value as an element of new furnace installations.

It has been found that the method of this invention is highly eflicient, the proportion of hydrocarbon converted to carbon monoxide and hydrogen being often as high as 70 to The residual gases as they leave the molten metal may be collected and, since they are combustible, may be burnt to provide auxiliary heat to the furnace, thereby reducing the fuel requirements of the burner used to fire the furnace, or may be used to promote heat elsewhere.

A form of apparatus for carrying out the process of the invention is illustrated in the accompanying drawing.

FIG. 1 shows a typical rotary furnace A as used in copper refining. This type of furnace is supported on rollers 21 and may be rotated by a suitable motor connected to a wing gear 22. Steam is brought to the furnace via a pipe 1 and is controlled by a pressure regulator 2 which keeps the steam in the loader pipe 4 at a constant pressure. Steam feed to each lance is controlled by individual valves 3 and is connected to the lance with a flexible hose 5. A hydrocarbon, such as propane or butane, is brought to the furnace via pipe 7 and controlled by a main valve 8. The feed to each lance from a common loader pipe 10 is also controlled by individual valves 9 and connected to the lance by flexible hose 11. The lance assembly consists of a mixing T 6 into which the steam and hydrocarbon is introduced, lance hanger 15, lance bushing 12 and lance 14. The lance slip-bushing 12 allows the lance to be manually or mechanically rotated periodically through about the lance axis in order to compensate for upward bending of the lance tip. The lance hanger is designed to suspend the lance at the proper angle for maximum depth of lance orifice 17 under the melt surface 19. The whole assembly is suspended to a suitable support by a hook 16 and cable or rope 24.

The lances in FIG. 1 are shown introduced through openings 18 in the end walls 13 of the furnace. However, it is also understood that the lance may be introduced through any openings in the furnace that are found suitable, such as openings around the cylindrical shell of the furnace 23.

It is further understood that this process may also be applied to other types of furnace such as a reverberatory furnace, a section of which is shown in FIG. 2, with a lance introduced through a sideport 18 in the wall 25 of the furnace. One or more of these lances may be introduced into a reverberatory furnace through suitable ports along one of the long sides of the furnace. For example it has been found that when using propane and steam, 3 or 4 such lances are required for treating a 200-300 ton charge of copper in a reverberatory furnace within a period of two to three hours.

The reaction between steam and hydrocarbon to form various reducing gases (commonly known as reforming reaction) takes place partially in the lance 14 and partially in the melt 20. Thus the gases emerging from the lance orifice 17 may not be completely reacted but will simultaneously continue to react to form reducing gases such as H and CO which, at the same time, react with oxygen in the copper as the gas mixture rises through the melt to the surface 19 to form CO and H 0. In addition to the benefit achieved by the production of reducing gases within the lance and in the melt, by the addition of steam, carbon is prevented from forming which would otherwise be deposited against the inner wall of the lance creating complete blockage and could also form a thick cloud of smoke at the vent opening of the furnace, both of which conditions are undesirable in the deoxidation process. Steam may be added in any proportion to the amount of hydrocarbon as seen fit by the personnel operating the furnace, or as established by special tests. However, the proportion of steam to hydrocarbon must be equal or less than the stoichiometric requirement for the reforming reaction. For instance, in the case of propane, the stoichiometric H O/propane ratio is 3:1 and, therefore, the proportion of steam to propane must be kept to less than 3:1 ratio.

The following reactions are shown for the introduction of steam in the hydrocarbon flow through the lance or tuyere to achieve the partial reforming of the hydrocarbon to hydrogen and carbon monoxide:

FIG. 3 is a section of the lance of the present invention, as it is introduced into a metal melt 20. Water or other liquid such as naphtha is delivered through an inlet tube 34 and end adapter 35 to a mixing and atomizing nozzle 36 and into the lance 14 through an orifice 37. The gas to be introduced into the molten metal is delivered to the lance 14 through an opening 33 in a mixing T 6 and passes through the atomizingtand mixing nozzle 36 into the lance 14 through orifice 38. The orifices 38 are so shaped and dimensioned that water enters the lance 14 in the form of a fine spray. As the mixture of water droplets and gases pass through the lance 14, in the process of copper deoxidation, the water is vaporized and reacts with the hydrocarbon gases in the lower hot section of the lance.

EXAMPLES Using apparatus as shown in the accompanying drawing three of the pilot scale tests were carried out using propane as the hydrocarbon and anode copper as the metal under treatment. The following table sets out the conditions of the tests and the results obtained:

Run Number Copper charge, 1b 4, 850 4, 630 4, 410 Lance, internal diameter, inches 5 Lance immersion in liquid bath, inche 7 7 7 Propane rate, cubic feet per minute..- 2. 3 3.0 4 Steam rate, cubic feet per minute 7 9. 0 4. 6 Time of reduction, min 56 45 20 Initial oxygen content, percent 9 1. 1 .65 Final oxygen content, percent. 09 O4 22 Total oxygen removed, percent. 81 1. 06 43 Rate of oxygen removed, lb./min 65 .82 .95 Gas utilization efficiency, percent:

From metal analysis 69 62 61 From gas analysis 77 69 These examples were conducted in a pilot reverberatory furnace on a 2 /2 ton metal blister copper which had previously been oxidized. Each reduction run was followed by a reoxidation period. The reduction gas, namely a propane-steam mixture, was introduced into the melt through a lance made of 310 stainless steel lowered vertically in the bath through the furnace roof. The depth of immersion of the lance was about 7" and the total depth of the molten bath at that location was 12". Lances of /2 A and 1" internal diameter were used.

The course of the reaction was followed by visual inspection of button samples and immersion and the examination of polished sections. The furnace gases were also analyzed chromatographically for carbon monoxide and carbon dioxide content during the run at three minute intervals. The samples were subsequently analyzed for oxygen content and the results appear on the above table.

In reference to the figures given for utilization efficiency it is pointed out that the efiiciency involves two elements:

(a) the efficiency of the propane-steam reactions:

C H +3H O 3CO+7H (1) (b) the efficiency of utilization of the hydrogen and carbon monoxide produced by reaction (1) in reducing oxidized anode copper:

In practice, it is difiicult to distinguish between the yields of reaction (1) and reactions (2) and '(3). In this specification, the term percent utilization efficiency indicates the combined yield of reactions (1), (2) and (3). Therefore, at the ideal situation of gas utilization ef- -ficiency, the propane would be completely converted to hydrogen and carbon monoxide and these gases would be fully utilized according to Equations 2 and 3.

It will be observed from the foregoing table that under the best conditions a ga utilization efficiency of the order of 70% is achieved.

It will be seen that the process of the present invention includes the advantages that it eliminates the need for a reforming plant and it eliminates the generation of any significant amounts of carbon soot. It also enables reforming within the body of the injection lance and the melt by introducing a mixture of gas-steam into the lance. The special lance construction used in the process allows for periodic rotation of It is apparent that the process herein described represents a significant advance in the field of gaseous deoxidation of molten metal.

We claim:

1. A process for the deoxidation of a molten copper, which process comprises injecting into a bath of said molten copper below the upper surface of said bath a mixture of a reformable hydrocarbon and steam whereby to achieve at least partial reforming thereof in situ to a reducing gas mixture containing carbon monoxide and hydrogen, said injection being effected through injection means, said partial reforming being at least partly effected in said injection means during said injections.

2. The process of claim 1 wherein said mixture of said reformable hydrocarbon and steam is gaseous.

3. The process of claim 1 wherein said reformable h'ydrocarbon is a normally gaseous aliphatic hydrocarbon.

4. The process of claim 1 wherein the reformable hydrocarbon is methane, ethane, propane or butane.

5. The process of claim 1 wherein the reformable hydrocarbon is a normally liquid hydrocarbon.

6. The process of claim 1 wherein said partial reforming reaction is at least partly effected during dispersion of said gaseous mixture through said molten bath.

7. The process of claim 5 wherein said injection is effected by introducing said liquid hydrocarbon into a stream of steam which is then injected below said surface.

8. The process of claim 1 effected in a cylindrical tilting anode furnace.

9. The process of claim 1 effected in a reverberatory anode furnace while simultaneously cooling the injecting means.

10. The process of claim 9 wherein said cooling is effected by water or other liquid spray introduced in the injecting means.

References Cited UNITED STATES PATENTS 0,057,969 7/ 1866 Reese 266--25X 3,115,405 12/1963 Boyd 75-60X 3,427,151 2/ 1969 Koudelka 75--60X OTHER REFERENCES De-Oxidation of Blister Copper in Metal Industry, pp. 87-88, Jan. 17, 19 63.

L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R. 

